Variable resistor device



March ll, 1947. D, G, C, LUCK 2,417,311

VARIABLE RESISTOR DEVICE Filed March 31, 1945 fyi INVEN mented Mu'. 1i, -1947 A VARIABLE RESISTOR DEVICE David G. C. Luck, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaw Application March 31, 1945, Serial No. 585,954

Ihis invention relates to variable resistor devices, and more particularly to electrical devices of the variable resistor type for the generation of speciiied mathematical or empirical functional relations, such as are used in certain electrical computer systems.

'I'he principal object of the instant invention is to provide an improved variable resistor structure which may be designed readily to provide a predetermined resistance vs. angular rotation characteristic.

Another object is to provide a device of the described type in which the desired resistancerotation characteristic may be attained to a great degree of accuracy and accurately maintained under conditions of continuous operation.

A further object of the present invention is to 7 claims. (CL ce1-ss) provide devices of the described type which will easily provide resistance-rotation characteristics which are diicult or impossible. to achieve with conventional prior art structures.

These and other objects will become apparent to those skilled in the art upon consideration of the following description, with reference to the accompanying drawing, of which Figure 1 is a front elevation of one embodiment of the invention,

Figure -2 is a side elevation of the device shown in Figure 1,

Figure 3 is a front elevation of a modification oi' the device shown in Figure 1,

Figure 4 is a side elevation of the structure of Figure 3,

Figure 5 is an illustration of one type of resistor element which may be used in the structures of Figures 1 and 3,

Figure 6 is a schematic diagram of a modiiication of the structures of Figures 1 and 3, and

Figure 7 is a front elevation of a modification of the structure of Figure 3.

Variable resistors are used quite generally for the purpose of controlling voltage or current in accordance with a predetermined function of the angular position of a shaft. The usual volume control of a conventional radio receiver is one example of such use. The accuracy of the relationship between shaft position and output-tolnput voltage ratio is a secondary matter in the ordinary radio receiver.

Certain other applications of variable resistors require that the resistance-rotation characteristic be maintained very closely to secure successful operation of the system. For example, some types of electrical computer systems employ variible resistors in such manner that the precision l by means of screws 2I.

of the computer is directly related to that of the resistor. Furthermore, the relationship between resistance and rotation may not be a continuously increasing or decreasing-function, as in the radio volume control, but may increase through one portion of the angular range of shaft rotation and decrease through another portion. The required function may be such that the resistance should change very gradually, or not at all, throughout some substantial angle of shaft rotation. Requirements of this nature are diflicultl to meet with variable resistors of prior art types, usually necessitating mechanical complexities such as cam drives between the control shaft and the variable resistor.

According to the present invention, a substantially linear resistance element is used in cooperation with a line contact device instead of the usual contact device in which the same contact point or surface touches the resistor at all shaft positions. It is proposed to move the resistor element and the contact elementy relatively to each other in such manner that a different portion'of the'contact line touches the resistor at each different position of the control shaft. It is then a relatively simple matter to design the device to provide substantially any desired resistance-rotation characteristic, by making the contact line follow a correspondingly predetermined curve.

Refer to Figures i and 2. A shaft I is mounted for rotation in al bearing 3 secured in a supporting plate 5. lA contact plate 1 is supported parallel to the plate 5 by spacer members 9 secured to the plates 5 and l. A hole I I is provided in the plate 7. The shaft I extends through the hole II, and supports near its outer end an arm I3. The arm I3 extends substantially radially of the shaft I and is secured thereto by a conventional collar and set-screw arrangement. The arm I3 is provided with an oiset extension l5 having a pair Aof lugs I'Istanding at right angles thereto, approximately parallel to the shaft I.

A rod ,I 9 is supported pivotally upon the lugs I'I A pair of bracket members 23 are secured to respective ends of the rod I9, and support between their outer ends a pair of strips 25. A strip-like resistor element 21, shown more clearly in Figure 5, is. clamped between the strips 25. The resistor element comprises a strip of insulating material 29, wound throughout the major portion of its length with resistance wire 3|. It will be apparent without further illustration that the resistor 2l may comdriving means.

prise a solid body of resistive material, rather than a wire wound element.

The proportions of the structure are such that the edge of the resistor 21 which faces the contact plate 1 runs substantially radially of the shaft I. A leaf spring 33 is secured to one of the strips 25v and bears against the member I6 to urge the resistor assembly toward the contact plate 1.

The ends of the resistor 21 are connected to Wires 35 and 31, which extend through the hole il to a pair of slip rings 39 and M, respectively. The rings 39 and M are mounted on a body t3 of insulating material secured to the shaft i. A

l pair of brushes l and 49 are mounted on a block' 5I of insulating material, in contact with the rings 39 and 4 I respectively. 1

The plate 1 is provided with a contact rib 53 which stands up from the plate 1 in the direction of the resistor element 21. The rib 53 is laid out in a curve corresponding in shape'to the polar graph of the desired resistance-rotation characteristic. In the present illustration this curve is a limacon, corresponding to the equation device, the The position of the point longitudinally of the resistor 21 depends upon the angular position lof the shaft I. The resistance which appears be'- tween the terminal 55 and the contact brush. is proportional tothe distance of the vpoint of contact from the inner end of the resistor A21.

Thus as the 'shaft I is rotated. the resistance be' tween the terminal 55 and the contact ..45 will vary in proportion to a-l-b sin o, where 0 'is the angular position of the shaft I- with respect to a reference line. (The line A-A in Figure l.) If a voltage E is applied betweenthe contacts 4B and I9, the voltage between the terminal 56 and the contact 45 will be l With the structure shown in Figures 1 and.2, the shaft l may be rotated continuously in one direction to lprovide cyclical repetition of the function. The described curve is particularly useful in providing a sine or cosine function, 'since the constantterm `a maybe cancelled by providing an additional .fixed voltage E\"='aE in series with the`connection to the contact l5 or the terminal 55, in proper polarity to oppose the constant component aE of the voltage E'. The

same thing may be accomplished byestablishing a the point at radius a on element 21 at reference potential, as by providing a grounded tap. fixed on the element at that radius and taking the output voltage between the rib 53 and ground. The

cosine function is readily provided by moving the reference line 90. This may be done by altering the angular position ofthe arml i3 on the shaft I rotating the contact plate 1 throughk 90, or by changing` the connection' of the shaft'l to its In the event that a continuously repeating function is' not required, the structure shown in may be preferred. In this case a contact rib 53 is embossed or otherwise formed on the surface of athin metal sheet 51. The sheet 51 is provided with extensions 59 which are secured to a blockv 6| of insulation. The top and bottom edges of the main portion of the sheet 51 are bent back tofo rm stiening flanges B0. The block 6I carries a shaft supporting member 83, through which a shaft 65 extends. A radial arm 81 is secured to the shaft 85, and supports a radially extending resistor element B9 parallel to the sheet 51 and in contact with the rib 53.

The operation of the structure of Figure 3 is substantially identical with that of the device of Figure 1, with the exception that the angular range of operation is limited to about The extensions 59 on the member 51 serve as leaf springs, maintaining contact between the rib 53 and the edge of the resistor element 69. It should be noted that this structure, like that of Figure l, can be made to increase and'decrease resistance during rotation of the control shaft in one direction, and will operate without diiiiculty with functions requiring a portion. of low or zero change of resistance with rotation.

In some cases it may be necessary to vary resistance in accordance with a function which changes very rapidly with rotation through a portion of the operating range. Figure 6 shows schematically a typical curve 10 which might be required. 'I'he rate of change of radius (or resistance) with respect to 0 is very low at 4the angle 01, but increases with increase in 0 through the values 02, 0:, etc., becoming a maximum at 0s.

If a rectilinear resistor element, extending radially from the origin, were used,as shown in Figures 3 and 4 Figures 1 and 4, the angle between the resistor element and the contact line would be relatively acute at the position 05. This is disadvantageous because the areas of the resistor and' the rib which are in contact with each other are much larger when the angle is relatively acute.

The contact angle o may be maintained. at substantlally 90 for all values of the angle 0 by curving the resistor strip as indicated by the line 1I. The curvature of the line 'l'l is a function of that of the curve 10, andl may bey made` so that the crossing angle is exactly 90 at all times. It shouldbe noted that the curve 10 isno longer a true polar graph of .the

ture of the curve 1I from a radial line.

It is preferable in practice to use aA rectilinear resistance lelement rather than a curved one even' under the conditions'illustrated in Figure 7. A crossing angle sufficiently close to 90 for practical purposes may be obtained by using the rectilinear approximation of the curve 1'|. This is indicated bythe dash'y line 13, which intersects the curve 1| at two points 15 and 11, and deviates from the curve 1I by the same amount at the center and at the extremes of the operating range. It isapparent that the maximum deviation of the crossing angle 'from 90 small.

Figure 'l shows a structure similar to that of Figure 4, but with the resistor element offset as described in connection with Figure 6 to provide lminimum variation of contact angle. The ref-v has been described as 'an imresistor devices, wherein resistor element is used required function lbut f must be distorted in accordance withjthe deparis relatively tively to each other so that a dili'erent portion of the contact line touches the resistor at each diiierent position of the control shaft. The contact line is made in a curve having a shape predetermined in accordance with the required resistance-rotation characteristic. y

I claim as my invention:

1. An electrical device comprising a substanitscontact portion extending radially of said shaft and in contact with said rib.

tially rectilinear resistor element, a contactl member having the shape of a polar graph of a predetermined voltage ratio vs. rotation characteristic to be provided by said device, means supporting said resistor element in radial relation to said contact member, and `means for rotating said resistor in contact with said contact member.

2. An electrical device comprising a resistor element including a substantially rectilinear contact portion, a contact body having araised rib of conductive material thereon. said rib lying along a line which is the shape of a polar graph of a predetermined resistance vs. rotation characteristic to be provided by said device, means 1 supporting said resistor element with said contact portion radially ofthe line of said rib and in contact with said rib, and means Vfor rotating said resistor element about the point corresponding to the origin of said graph, whereby the resistance between one end-of said resistor element and said contact body varies as said predetermined characteristic.-

3. An electrical device comprising a linear resistor element, a contact 'member having a curved shape predetermined in accordance with y a voltage ratio vs. rotation characteristic tobe provided by said device. means supporting said resistor element in contact with s'ald contact member, and means for rotating said resistor about an axis substantially perpendicular to the plane of the curve of said contact member.

4. An electrical device comprising a contact body having a raised rib oi' conductive material thereon, said rib lying along a curve which is the shape of a polar graph of a predetermined resistance vs. rotation characteristic to be provided by said device, a shaft perpendicular to the plane of said line, with its axis through the origin oi' said polar graph, a resistor element including a substantially linear contact portion, and means supporting said resistor element with 5. An electrical device including a contact member having the coniiguration of a polar graph of an electrical flmction to be generated, a-shaft perpendicular to the plane of said member, with its axis extending through theorigin of said polar graph, aresistor element having a substantially linear contact surface, an arm secured to said shaft and extending at a right angle thereto, ymeans supporting said resistor element on said arm with its said-contact surface cxtendingradially of said arm, and spring means urging said resistor element in a direction substantially parallel to the axis of said shaft toward said contact member. A

6. An electrical device including a contact member having the configuration of a polar graph of an electrical function to be generated, a shaft perpendicular to the plane of said member, with its axis extending through the origin of said polar graph, a resistor element having -a substantially linearcontact surface, an arm secured to said shaft and extending at a right angle thereto, and means supporting said resistor element on said arm with its said contact surface extending radially of said arm.l

7. An electrical .device including a contact member having the configuration of a polar graph of an electrical function to be generated, a shaft perpendicular to the4 plane of said member, with its axis extending through the origin of said polar graph, a resistorelement having a substantially linear contact surface, an arm secured to said shaft and extending at a right angle thereto, means supporting said resistor element on said arm with its said contact surface extending radially oi' said arm, and spring means urging said contact member toward said resistor element in a direction substantially parallel to the axis of said shaft. Y n

DAVIDG. C. LUCK.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS 

